This invention concerns a friction bearing for deep well drilling tools, especially drill bit direct drives.
In a known friction bearing for deep well drilling tools, a trace ring is provided (US Defensive Publication T102 901) having a ring-shaped bearing body of steel and prefabricated cylindrical bodies mounted in axial boreholes of the bearing body and having a bearing layer of polycrystalline diamond and a support layer of a sintered material. The molded bodies are placed in a ring-shaped arrangement in the trace ring with their diamond layer that is provided with a conical taper projecting above the surface of the supporting body and forming a sliding plane composed of adjacent ring-shaped sliding surfaces. The bearing ring in turn has cylindrical molded bodies provided with a polycrystalline diamond layer at the surface and set in a ring as bearing segments that are supported on the sliding surface of the trace ring.
Such a design is associated with load conditions that change constantly because the surfaces that are in mutual engagement change constantly and greatly during one complete revolution. A friction bearing with such a design of the trace ring is therefore limited in its load bearing capacity and is subject to a great deal of wear.
In another known friction bearing (German Patent No. 3,513,124), the trace ring has a cohesive ring-shaped slide way in the form of a seat of a sintered metal powder ceramic material or polycrystalline diamond material. Such a trace ring can withstand high loads and operates under uniform load conditions but is expensive to manufacture because the seat cannot be prefabricated but instead can only be manufactured by sintering it as a whole onto the support body in a separate operation.
This invention is based on the goal of creating a friction bearing that can withstand high loads, is subject to little wear and can be manufactured under favorable conditions.
With the friction bearing according to this invention, the surfaces of the molded bodies form an essentially closed ring channel with the result that the contact surface between the friction bodies of the bearing ring and the ring channel of the trace ring do not undergo any mentionable changes during one revolution of the bearing. Accordingly, the friction bearing can withstand high loads and also shows little wear due to the essentially uniform load conditions. Furthermore, the mosaic-like arrangement makes it possible to use molded bodies consisting of blanks of partially worn cutting elements of rotary drill bits. This is especially the case in one version where the surfaces of the molded bodies are bordered by arc sections, because such molded bodies can be cut from circular cutting elements which are preferred in rotary drill bits and are usually worn on one side.